1. Field of the Invention
This invention relates to a fluid sealed type antivibration rubber device such as a suspension mount rubber and an engine mount rubber of an automobile vehicle which controls the internal pressure by an external means.
2. Description of the Background Art
Such a fluid sealed type antivibration rubber device is known and disclosed for example in Japanese Laid-Open Utility Model Publication (Kokai) No. Hei 3-46035 in which a rotating member is provided in a fluid chamber and the internal pressure therein is mechanically controlled by rotating the rotating member. Another approach is disclosed in Japanese Laid-Open Patent Publication (Kokai) No. Hei 5-172180 in which the internal pressure is electrically controlled by vibrating a vibrating portion such as bellows which are electromagnetically driven.
In the mechanically controlled fluid sealed type antivibration rubber device using the rotating member, disadvantages may be found in that the construction becomes complicated, many numbers of parts are necessary and the change of performance during use is quite big because it is difficult to secure both the durability and the sealing in a rotating portion of the rotating member.
On the other hand, the electrically controlled fluid sealed type antivibration rubber device has also the disadvantages that the construction becomes complicated, many numbers of parts are necessary, and it is difficult to ensure the performance because the performance of magnetic fluid used as working fluid varies with a change in temperature and the working fluid changes with the passage of time.
In addition, since the periphery of the vibrating portion such as the bellows is immersed in the working fluid, the fluid resistance resulting from the vibration of the vibrating portion increases and as a result, the consumption amount of the necessary driving electric power increases and the sealing is also difficult.
Further, such a fluid sealed type antivibration rubber device is generally required to exhibit vibration-damping in a low frequency range of 9.about.15 Hz, to exhibit an extreme low dynamic spring rate in idling vibrations of an engine in a frequency range of 20.about.30 Hz and also to exhibit a moderate low dynamic spring rate for the principal frequency vibrations of higher than 30 Hz during running of the automobile vehicle at a constant speed. Thus, the fluid sealed type antivibration rubber device is required to selectively find the most suitable control depending upon such actual running conditions of the vehicle as stated above.
It is therefore an object of the present invention to provide an improved fluid sealed type antivibration rubber device which can overcome all of such drawbacks as found in the prior art.